US1680410A - Relay-tripping system - Google Patents

Description

. Aug. 14, 1928.

L. N. CRICHTON ET AL RELAY 'IRIPPING SYSTEM Filed May 24. 1921 w d Rm 00 m mfi ECR V 0 M e e c h n 5 6V Mr W a L AONE Patented Aug. 14, 1928.

UNITED STATES PATENT OFFICE nnsnm N. 'cnrcn'ron, or nnenwoon, arm LAWRENCE n. GOLLADAY, or wmxms- BURQ}, PENNSYLVANIA, ASSIGNOBS TO -WES'1INGHOUSE ELECTR IC AND MANUFAC- TUBING comm, A conromrron or rannsnvamn.

nnnaY-rmrrme srsrau.

Application filed Kay 24,

Another object of'our invention is to vide a relay system, ofthe above-indicated character, that shall co-operate with a current transformer, energized from the circuit to be protected, in such manner that normally'no load will be placed upon the current transformer but energy will be derived therefrom to ener 'ze a trip coil only upon the occurrence of predetermined abnormal conditions. i

Another objectof our invention is to provide a relay tripping system, of the aboveindicated character, that shall embody a resonant circuit whereby normally no load will be placed upon the-current transformer until the predetermined abnormal conditions occur, whereupon the tri coil will be connected to an element ,of t e resonant circuit in such manner as to be energized from the current transformer. I

A further object of ourinvention is to provide a relay tripping-system of the aboveindicated character thatshall be simple in arrangement and effective in its operatlon.

In systems heretofore employed for deriving-tripping energy from a current transformer to be protected,"v arious devices have been employed to control the connection of a. trip coil to the current transformer upon the occurrence of redetermined abnormal conditions. Such evices have been so disposed as to be continuously energized, and a load'was thus always-placed upon the cur-' .renttransform'er.

Inview of that condition, a system embodying our invention comprises a resonant circuit including a current transformer, a condensive reactor and an inductive reactor. Although the potential difierence'across the terminals of either reactor might be relatively large, the load on the current transformer and, consequently, the potential dif- 1921 Serial ll'o. 472,151,

nect the trip coil of a circuit interrupter across the terminals of either reactor upon the occurre cc of predetermined abnormal conditions, it'ective protection of the circuit may be obtained, and actuating energy for the interrupter may be derived from the circuit to be protected without placing a continuous load upon the current transformer; In such a system, the elimination of the load placed upon the current transformer by, the controlling devices would liU render measuring instruments connected to the current transformer more accuate by reason of thelesser load on the transformer. The accompanymg drawing is a diagrammatic view of a relay trippmg system embodying our invention.

Referring to the drawing, a source 1 of electromotive force supplies energy to a circuit 2 through a. circuit interrupter 3. Upon the occurrence of abnormal conditions in the circuit 2, such as extremeoverload or shortcircuit, the interrupter 3 is adapted to be actuated by a tripping mechanism 4, the energization of which'is controlled by a relay tripping system 5. v Y

The relay system 5 comprises the secondary winding 6 of a current transformer 7, the primary winding 8 of which is connected in the mainicirc-uit. The secondary winding 6 of the current transformer is connected in circuit with the winding of an electrical instrument 9, the fwindin ;of a relay 10, an inductive reactor 11 an a condensive -re- .actpr 12.1

- The relay 10 is preferably. of the induction disc type embodying-an inverse tinieelement and, when energized to a predetermined degree, is adapted toeffect the enga ement of apair of contactmembers 13 and 14. .The instrument 9 and the relay 10 serve to increase the value of inductive reactance of the relay system, and, if desired, may be arranged to constitute the entire inductive reactance.

"1 The reactive elements 9, 10, 11 and 12 are circuit therewith that the circuit normally is rendered resonant. Upon the occurrence of such abnormal conditions in the load circuit 2 as suffice to efiect the engagement of the contact members 13 and 14, the trip coil 4 is connectedacross-the condensive reactor 12, whereupon the resonant condition of thecircuitis disturbed and suflicient energy is thereupon derived from the main circuit,

through the current transformer 7, to energize the trip coil 4:.

It will be observed that, until the resonant condition is disturbed by the connection of the trip coil across'the terminals of the condensive reactor 12, no load is placed upon the current transformer except'by the measuring instrument 9 and the relay 10. In the system illustrated, the inductive reactance of the instrument 9 and of the relay 10 contribute to the inductive reactance-of the resonant circuit.

'It will thus be observed that substantially no load is normally placed upon the current transformer by auxiliary control devices which are employed to provide a potential difference for energizing the trip coil, but only upon the occurrence of predetermined abnormal conditions, such as overloads of predetermined values, or short-circuits-will a large load be placed upon the current transformer.

It is understood that various other arrangements of the elements described and illustrated may be made within the spirit and scope of the invention, as set forth in the appended'claim.

We claim as our invention:

In an electric circuit, the combination with a circuit-interrupter provided with a* trip coil controlling said circuit, of a current transformer connected in said circuit, a relay, a winding for said relay and a condenser connected in series with the secondary wind-- subscribed our names this 11th day of May,

LESLIE N. CRICHTON. LAWRENCE R. GOLLADAY-

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